Near field communication (“NFC”) devices are capable of communicating when they are placed in close proximity to each other, and may be used for transactions such as payment transactions. Each of the NFC communication devices includes an antenna and related circuitry such as a matching circuit. A first NFC communication device generates a wireless carrier signal at a suitable frequency such as 13.56 MHz and transmits that signal over its antenna. When the antenna of a second NFC communication device is placed in close proximity to the antenna of the first NFC communication device, the two devices become inductively coupled, such that energy is coupled between the two devices through a shared magnetic field.
An NFC device may be a NFC transmitter that provides a signal such as a carrier signal or a modulated version of the carrier signal based on data. The signal may be provided by circuitry and may have a phase, amplitude, waveform, and other characteristics. For example, a signal may initially be generated by circuitry such as a processor and may be a square wave at the carrier frequency, with amplitude and/or frequency provided on the output signal from the processor or by other circuitry. In some embodiments, additional circuitry may perform functions such as applying modulation to the carrier signal, tuning the antenna of the transmitter, and modifying the waveform of the signal to be transmitted. This additional circuitry may modify the phase of the signal as it is processed before being transmitted, such that an original signal provided by processing circuitry may have a different phase from the signal that is actually transmitted from the antenna.